1. Field
Embodiments of the present disclosure relate to a glass composition for a ceramic phosphor plate and a ceramic phosphor plate manufacturing by using the glass composition.
2. Background
A white LED (Light Emitting Diode) is in the spotlight as a light source for white lighting having high efficiency and high reliability and has been already used as a small sized light source having small power consumption. Even though there are various methods of implementing a white LED, the most commonly used method is a method of molding a blue LED element with a matrix made of resin with a yellow phosphor. However, since blue light has strong energy, it may easily cause deterioration of the resin. Accordingly, since the white LED having such a structure causes discoloration of the resin when being used for a long time, the color of light emitted from the white LED is changed. Also, since the molding is performed with resin, heat emission from the element may not be easily performed, so it is easy to increase a temperature. Due to this increase of the temperature, it is problematic in that the color of emitted light is changed to yellow.
In order to solve these problems, a phosphor plate in which a ceramic pellet is used as the matrix material of a phosphor has been applied. The phosphor used in such a phosphor plate is only limited to an oxide phosphor, in particular, a YAG (Yttrium Aluminum Garnet) phosphor. When merely the oxide phosphor is used, it is difficult to implement various color coordinates and color temperatures. Also, when merely a phosphor such as a YAG and the like is applied, a heat-resisting temperature is required to be 800 °C. or more, and accordingly, the compositional condition of glass is not needed to become complicated. However, in order to implement various color temperatures, a red phosphor and a yellow phosphor should be mixed in an appropriate amount. To do so, there is a need to adjust the compositional condition of glass in order to reduce a sintering temperature because these phosphors are vulnerable to heat.
However, when the phosphor plate is used for a long time, the transmittance of glass may be deteriorated and whitening in which a surface of the phosphor plate becomes hazy may be generated due to a compositional reaction of moisture and the glass in terms of properties of the materials (see FIG. 1). With regard to the whitening, elements based on B, Na, and Li may have an influence on the whitening. However, in particular, it is known that a hydrate is easily formed by Na. FIG. 2 shows a mechanism that a whitening phenomenon is generated by the formation of a hydrate due to moisture and glass elements, in particular, Na.